SPERRY ON METACRINUS. 19-'> 



NOTES ON METACRINUS. 



HY W. L. SPERRY;, OLIVET COLLEGE. 



The genus Metacrinus as described by Carpenter, who classified the 

 ^'Challenger" orinoids, is distinguished from the rest of the stalked 

 crinoids by the number of radials. There are from four to six, the second 

 and fourth joints being syzygies, or immovable sutural unions between 

 two joints. 



The specimens under consideration were dredged by the "Albatross" in 

 Suruga Gulf, Honshu Island, Japan, during the summer of 1900. About 

 a hundred individuals Avere taken from a bottom of volcanic sand, shells, 

 and rock and about thirty were sent to Olivet for classification. Except 

 for a few individual variations as to the number of radials, distichals, 

 and palmars, and the size and color they seem to be the same in every 

 particular. Carpenter recognizes thirteen species of Metacrinus and there 

 are three of these s])ecies to whii'li the individuals of the "Albatross" col- 

 lection will answer perfectly, rniiindns, interrupt us, and an unnamed 

 species dredged by the Swedish v^essel "Vega" and commonly known as 

 the "Vega" specimen. Carpenter recognizes the similarity between these 

 three species yet has based his classification on what seems to be merely 

 individual variation. 



The most important distinction he makes between interruptus and 

 rotundus is in the number of radials. In interruptus there are six 

 radials, the second and fourth joints being syzygies, while in rotundus 

 the number varies, usually there are five or six, the second and often the 

 fourth syzygies. The fact that he had but one specimen of each would 

 have made it impossible for him to study variation in this respect and 

 he might easily have supposed them to have been two different species. 

 According to Carpenter's definition rotundus is distinguished from all 

 other species by the fact that the apposed surfaces of the nodal and 

 infra-nodal joints are circular; cimilar surfaces in intcn-uptus are 

 pentagonal. This distinction, while perhaps important, seems in many 

 cases to depend largely on the age of the individual and the portion of 

 the stalk examined. In the older individuals the action of the water 

 has tended to modify the pentagonal form of the stalk so characteristic 

 of the younger individuals, until, in many cases, the base of the stalk 

 has become perfectly round. The growing part of the stalk, i. e. the first 

 twelve or thirteen nodes, is always sharply pentagonal in outline, and as 

 the individual Carpenter classified as interruptus was broken otf at 

 the nineteenth node, it is possible that the stalk was both too short and 

 too young to show the rounded appearance of the older and longer stalk 

 of rotundus. The "Vega" s])ecimen, from the stem of which Carpenter 

 had a few fragments, resembles very closely both rotundus and inter- 

 ruittus except that the stem joints "have a smaller diameter and a 

 greater height, both relatively and absolutely." 



